Well, it depends what you call spam, how well known your server is (are your email addresses spread far and wide on the web or only known to a couple of people) but a lot of spam is automated and algorithmic, so most servers will be showered with speculative mail addressed to likely mailboxes - which your server still has to process, if only to bounce the message; if you have antispam measures, your server can just drop the connection when it detects a spammy sender (e.g. from an address on a black or greylist). I’m not currently running any mail servers, but a few years back when I did, I used to get about 80% spam incoming.

Honestly, not all that bad. A lot of the spam is just the stuff from companies we gave our email, y’know, the usual.

There’s the occasional spam/scam email, every few days at most, but it’s pretty ignorable.

(we did set up rspamd purely for DKIM signing, and it might be filtering our inbound email, I don’t know.)

I ran an open smtp server for an experiment. Most of the email it got was more like probes than traditional spam.